Recording materials that employ color development through the reaction between a color-forming compound and  a color-developing agent allow recording in a short time using a relatively simple apparatus without performing complicated treatments such as development and fixation and are thus widely used in thermal recording paper for output recording in facsimiles, printers, etc., or pressure-sensitive copying paper or the like for forms for simultaneous multiple copying. These recording materials are required to immediately develop colors, maintain the whiteness of an uncolored part (hereinafter, referred to as a “background”), and offer the high colorfastness of colored images. Particularly, recording materials excellent in the light resistance of the background are desired in terms of long-term storage stability. For this purpose, attempts have been made to develop color-forming compounds, color-developing agents, storage stabilizers, etc. Nevertheless, recording materials that have well balanced, sufficiently satisfactory color-developing sensitivity, background and image stabilities, etc., have not been found yet.
Also, 2,4′-dihydroxydiphenylsulfone and 4-hydroxy 4′-isopropoxydiphenylsulfone have heretofore been known as recording materials excellent in background stability and are, however, still unsatisfactory in terms of, for example, the light resistance of the background.
The present inventors have already proposed a recording material excellent in the light resistance of the background using a cinnamamide compound as a color-developing agent (see patent document 1). However, this recording material is still not sufficiently satisfactory in terms of, for example, the heat resistance of images, and practical recording materials remain to be obtained.